refactor: apply minimal tfcode branding

- Rename packages/opencode → packages/tfcode (directory only)
- Rename bin/opencode → bin/tfcode (CLI binary)
- Rename .opencode → .tfcode (config directory)
- Update package.json name and bin field
- Update config directory path references (.tfcode)
- Keep internal code references as 'opencode' for easy upstream sync
- Keep @opencode-ai/* workspace package names

This minimal branding approach allows clean merges from upstream
opencode repository while providing tfcode branding for users.

packages/tfcode/src/lsp/launch.ts

@@ -0,0 +1,21 @@
+import type { ChildProcessWithoutNullStreams } from "child_process"
+import { Process } from "../util/process"
+
+type Child = Process.Child & ChildProcessWithoutNullStreams
+
+export function spawn(cmd: string, args: string[], opts?: Process.Options): Child
+export function spawn(cmd: string, opts?: Process.Options): Child
+export function spawn(cmd: string, argsOrOpts?: string[] | Process.Options, opts?: Process.Options) {
+  const args = Array.isArray(argsOrOpts) ? [...argsOrOpts] : []
+  const cfg = Array.isArray(argsOrOpts) ? opts : argsOrOpts
+  const proc = Process.spawn([cmd, ...args], {
+    ...(cfg ?? {}),
+    stdin: "pipe",
+    stdout: "pipe",
+    stderr: "pipe",
+  }) as Child
+
+  if (!proc.stdin || !proc.stdout || !proc.stderr) throw new Error("Process output not available")
+
+  return proc
+}